The present invention relates to methods for the production of leather, and more particularly to a process for producing leather from wet blue pig skins.
A wide variety of methods are used commercially for producing leather from skins or hides. In general, leather production involves three broad phases. First, the skins or hides are prepared for tanning. This generally involves curing the skins so that they do not begin to decompose before tanning. At the tannery, the skins are typically soaked in water to remove all water-soluble materials, such as salt, blood, and dirt, and to replace moisture lost in the curing process. Typically, the next step is to remove hair from the skins. Often, this is done by soaking the skins in a lime solution and then mechanically removing the hair, along with extraneous flesh and tissue, by machine. The next general step is xe2x80x9cdelimiting,xe2x80x9d which removes the lime introduced during the dehairing step. The deliming process involves soaking the skins in a mild acid solution. Bating may also occur at this time. Bating is a process in which the skins are treated with enzymes that make the skins soft and flexible and provide them with a smoother grain.
The bated skins are then tanned using any of a variety of conventional tanning methods. For example, the skins may be tanned in a mineral tanning process. In mineral tanning, the skins are soaked in a mineral tanning agent, typically the salt compound of chromium. To prepare the bated skins for chrome tanning, the skins are pickled in a conventional salt and acid brine. Once pickled, the skins are tumbled in a chromium-sulfate solution containing liquors that enhance the skins"" ability to absorb the tanning agent. Alternatively, the skins may be tanned in a vegetable tanning process. Vegetable tanning generally involves soaking the skins in a tannin solution containing liquors that improve and speed the absorption of tannin. Tannin is typically extracted from wood or bark, such as the chestnut wood or oak bark. The skins are soaked in successively stronger solutions until they have absorbed the appropriate amount of tannin for the particular application.
The tanned skins, which in the case of chrome tanned skins are sometimes referred to as xe2x80x9cwet blue leather,xe2x80x9d are then subjected to a variety of treatments that provide the skins with the desired characteristics. For example, the skins can be lubricated using a blend of oils and greases, and dyed to the desired color through drum dyeing, spraying, brush dyeing or staining processes. In some applications, the skins are retanned to introduce additives that provide the skins with desirable characteristics. For example, waterproofing agents are typically introduced during a retanning process. Waterproofing is a particularly important characteristic in many applications, including footwear applications. The waterproofness of a leather is typically measured in Maeser flexes, which is essentially the number of flexes that a leather can undergo before it loses the waterproof characteristic. The waterproofness standard set by the U.S. military is 15,000 Maeser flexes. Further, heat resistant and flame resistant agents are often introduced prior to and/or during the retanning process. Finally, the skins are staked and finished. Staking is a mechanical softening process in which the skins are repeatedly beat by fingers. Finishing typically involves the application of a finishing compound, such as oil blend, to the surface of the leather. The above described processes are typical steps involved in the production, but are not exhaustive. Alternative and additional processes are commonplace in the leather production industry.
Although there are a variety of well-known techniques for obtaining leather with one or more desired characteristics, such as softness, suppleness, waterproofness, flame resistance, and heat resistance, it is difficult to produce leather that has the appropriate combination of these characteristics, In fact, these characteristics are achieved only by carefully controlling a complex series of variables in the production process. For example, the precise additive formulation, the quantity of additives, the mixture ratio of additives to water in the various steps, the temperature of the solutions in which the skins are treated, the running time in a given liquor bath and the pH level of the solutions in which the skins are treated are all crucial to the production process. As perhaps the result of these complexities, there remains an unmet need for leather that is highly waterproof, flame resistant and heat resistant and yet remains soft and supple.
The aforementioned problems are overcome by the present invention wherein a leather production process is provided which produces a leather that is highly waterproof, flame resistant and heat resistant and yet remains soft and supple. The production process generally includes the steps of: (a) providing wet blue, full grain skins, (b) applying a chromium or liquid chrome solution to the skins while at a pH of 3.5 or lower, (c) raising the pH level of the skins to 6.0 or above, (d) retanning the skins with a vegetable tanning agent, (e) introducing the skins to a dye bath, (f) introducing waterproofing lubricants into the dye bath, (g) fixing the dyestuff and waterproofing lubricants in the skins while reducing the pH level to the range of 3.3-3.8, (g) introducing the skins to a second dye bath, (h) fixing the dyestuff while reducing the pH level to a range of 3.0-3.5, (i) introducing the skins to a float containing an additional waterproofing agent, (j) fixing the waterproofing agent while reducing the pH level to approximately 3.0, (k) capping the skins to assure the fixation of penetrated waterproofing agents and to remove emulsifiers, (l) introducing the skins to a bath containing flame resistant agents, (m) drying the skins, (n) staking the skins, and (o) applying a waterproofing oil to the surface of the skins.
The present invention produces a soft and supple leather that is fire resistant, heat resistant and highly waterproof. This combination makes the leather particularly well-suited for a variety of application, including work footwear and motorcycle, ATV and other vehicle riding footwear. As described in more detail below, standard industry tests show that the leather produced using a preferred embodiment of the present invention provides a uniquely high combination of heat resistance, flame resistance, waterproofness and water vapor permeability.
These and other objects, advantages, and features of the invention will be readily understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings.